Hey Carm... here's the 'skinny': (with complimentary 'spellcheck' fixes!)
IF, after re-checking with these fine suggestions, you think that your galvo mirrors ARE bad - try sending a beam directly thru one of the galvo mirrors at 0 deg. incidence-angle (straight on) and see- VISIBLY (not metered)- if you get any significant (>5 mW out-of 100mW) 'pass-thru', - then repeat, with the galvo mirror at 45 deg. (careful with reflections! ‹(•¿x)› doh!) and if you are seeing a LOT of pass-thru (like say 30mW out-of 100mW), well, time to ask for replacement mirrors...
Also, try test again, MEASURING results reflecting OFF galvo mirror - ie: say coming out of laser X, you directly-measure 100mW (or whatever your powers are) of green, but off galvo-mirror bounce-tests, it is 40mW (and there is NOT 60mW of green VISIBLY-passing thru the galvo mirror out into the room - especially at 45 deg.), well, then time to discuss 'rated power @ Xnm' vs what you are measuring off those bounces, with the people that sold you the DPSS...
IF after these tests, you feel that the galvo mirrors ARE truly bad, AND your galvo manufacturer does not/can not help you (out of warranty, don't sell replacement mirs, etc), check with Fred or Amanda at One Stop Laser Shop (PL member "OSLS") - they have many types of galvo-replacement mirrors, and if your shafts can take a 1mm-thick mirror, they sell the best aerospace-grade broadband dielectric mirror we've ever used...
Hope this helps! ... peace.
- J